This process relates to an improved process for the preparation of 1,4-phenylenediamine using 1,4-dihydroxybenzene. p-Aminophenol can be aminated to 1,4-phenylenediamine with the same process. The process is accomplished in good yield at a temperature within the range of from about 300.degree. C. to 450.degree. C. at a pressure up to 3000 psig despite the fact that p-aminophenol, the intermediate compound in the amination of 1,4-dihydroxybenzene to 1,4-phenylenediamine sublimes and decomposes at temperatures within the range of from about 184.degree. C. to about 284.degree. C. and 760 mm pressure. The invented process is accordingly surprising although the direct amination of mono- and dihydroxybenzenes other than 1,4-dihydroxybenzene can be accomplished at temperatures within the range between 300.degree. C. and 570.degree. C., by the process taught by Becker, et al., U.S. Pat. No. 3,860,650. The preparation of 1,4-phenylenediamine from 1,4-dihydroxybenzene by the process taught by Becker U.S. Pat. No. 3,860,650 results in low uneconomical yields. The intermediate of p-aminophenol in conversion of 1,4-dihydroxybenzene to 1,4-phenylenediamine decomposes at the temperatures of 300.degree. C. to 570.degree. C. taught for the Becker U.S. Pat. No. 3,860,650 process.
Aromatic diamines are useful in the preparation of aromatic polyamides, polyimides and polyamideimides. Aromatic diamines are also well-known as being useful in the preparation of azo dye intermediates, photographic developing agents, fur dyes, agents for photochemical measurements, antioxidants for petroleum products, cellulose ethers and rubber.
Preparation of phenylenediamines has been by a number of processes which have been of two types; amination by reduction wherein a bond between a nitrogen and a ring carbon already exists in the molecule and amination by ammonolysis wherein a nitrogen is not already bonded to a ring carbon. The p-phenylenediamine is usually obtained by reduction of the parent nitro compound, p-nitroaniline, because of better yields, the need for avoiding contaminants, the sensitivity of the starting materials and final products to the conditions of the process. Reduction of the parent nitro compound requires preparation of the parent compound which involves a nitration step, usually of a chlorobenzene, which results in an ortho-para mixture. Amination by reduction and ammonolysis is performed with separation and purification of the isomers with consequent overall lowered yields. Consequently, for some time a more direct method of producing p-phenylenediamine has been sought.
I have found a method whereby 1,4-dihydroxybenzene can be converted to p-phenylenediamine in good yield without decomposition of the intermediate of p-aminophenol occurring and consequent loss of final product. The application of the process is directed only to the preparation of p-phenylenediamine from 1,4-dihydroxybenzene since aminophenols other than p-aminophenol do not decompose at the temperatures and pressures required for amination of 1,4-dihydroxybenzene.
It is already known that aniline-type compounds can be prepared by the liquid or vapor phase amination of certain phenolic compounds with ammonia. Generally, the reaction takes place at elevated pressures and temperatures between 300.degree. C. and 600.degree. C. in the presence of catalysts containing silica and alumina. These phenolic compounds or hydroxybenzenes can be unsubstituted or substituted so long as the substitutions do not interfere with the course of the reaction. Typical groups which can be attached to the benzene nucleus are alkyl or aryl groups. The type of catalyst employed and reaction conditions have been found to be of particular significance. For example, U.S. Pat. No. 3,860,650 to Becker et al. teaches the preparation of organic amines from certain phenolic-type compounds including hydroxybenzenes such as catechol, pyrolgallol and hydroquinone in the vapor or liquid phase at temperatures of from 300.degree. C. to 570.degree. C. in the presence of an alumina catalyst derived from a precipitated gel form and having a minimum alkali metal content which is achieved by leaching with acid. As an example, Becker recites the amination of a substituted phenolic-type compound, the preparation of 2,2-bis (p-aminophenyl) propane by the liquid phase amination of 4,4-isopropylidene bisphenol. Becker does not teach in an example the preparation of p-phenylenediamine using temperatures of from 300.degree. C. to 570.degree. C. U.S. Pat. No. 3,929,889 discloses the preparation in low yields of phenylenediamines predominantly meta or ortho and some quantities of para from aromatic monoamines such as aniline in the presence of a hydrogen transfer catalyst of a nickel/nickel oxide cataloreactant. In general, U.S. Pat. No. 3,929,889 teaches that cataloreactants and reaction conditions leading to higher conversion favor the predominant production of meta-phenylenediamines; those leading to lower conversion of aromatic monoamines favor the ortho-phenylenediamines. U.S. Pat. No. 3,931,298 also discloses a hydrogen transfer catalyst for the conversion of hydroxy aromatics to the corresponding aromatic amines with ammonia in the presence of a Group VIII metal hydrogen transfer catalyst with a cyclohexanone cocatalyst at a temperature of from about 200.degree.-400.degree. C. Liquid hydrocarbons can be used as solvents. Hydroquinone is recited as a starting material although preferred materials are mononuclear alkyl-substituted phenols. Japanese Pat. Nos. 74-14737 and 74-14738 teach methods of gas-phase preparation of aromatic amines and preparation of the gamma alumina catalysts used. p-Phenylenediamine is produced from hydroquinone in low yield as an example. The gamma alumina catalyst is required to be treated with a carboxylic acid to provide activity. Weakly acidic catalysts such as commercial gamma alumina without an acid treatment are stated to be too inactive to be of use. Alpha and eta aluminas are not to be used.
Accordingly, it is well-known in the prior art to aminate hydroxybenzenes usually to the monoamines, but an economical process for ammonolysis in high yields and good purity of 1,4-dihydroxybenzene to p-phenylenediamine has not been previously known. For example, a satisfactory process has yet to be developed for the ammonolysis of p-dichlorobenzene to the diamine by direct replacement of both chlorine atoms even though excellent yields can be obtained of the ortho compound from o-dichlorobenzene if the reactant is highly purified to remove the para compound. (Kirk-Othmer, Ency. of Chem. Tech., 2nd Edition, Interscience, Vol. 2, 1963, p. 361.)